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        <a href="../.." >7.CAS与atomic类.md</a>
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                                <div id="anchor-navigation-ex-navbar"><i class="fa fa-navicon"></i><ul><ul><li><span class="title-icon "></span><a href="#cas"><b></b>CAS</a></li><ul><li><span class="title-icon "></span><a href="#cas&#x5206;&#x6790;"><b></b>CAS&#x5206;&#x6790;</a></li><li><span class="title-icon "></span><a href="#cas&#x7F3A;&#x9677;"><b></b>CAS&#x7F3A;&#x9677;</a></li></ul><li><span class="title-icon "></span><a href="#atomic&#x65E0;&#x9501;&#x7C7B;"><b></b>atomic&#x65E0;&#x9501;&#x7C7B;</a></li></ul></ul></div><a href="#" id="anchorNavigationExGoTop"><i class="fa fa-arrow-up"></i></a><h2 id="cas"><a name="cas" class="anchor-navigation-ex-anchor" href="#cas"><i class="fa fa-link" aria-hidden="true"></i></a><a name="cas" class="plugin-anchor" href="#cas"><i class="fa fa-link" aria-hidden="true"></i></a>CAS</h2>
<p>CAS&#xFF0C;Compare And Swap&#xFF0C;&#x5373;&#x6BD4;&#x8F83;&#x5E76;&#x4EA4;&#x6362;&#x3002;Doug lea&#x5927;&#x795E;&#x5728;&#x540C;&#x6B65;&#x7EC4;&#x4EF6;&#x4E2D;&#x5927;&#x91CF;&#x4F7F;&#x7528;CAS&#x6280;&#x672F;&#x9B3C;&#x65A7;&#x795E;&#x5DE5;&#x5730;&#x5B9E;&#x73B0;&#x4E86;Java&#x591A;&#x7EBF;&#x7A0B;&#x7684;&#x5E76;&#x53D1;&#x64CD;&#x4F5C;&#x3002;&#x6574;&#x4E2A;AQS&#x540C;&#x6B65;&#x7EC4;&#x4EF6;&#x3001;Atomic&#x539F;&#x5B50;&#x7C7B;&#x64CD;&#x4F5C;&#x7B49;&#x7B49;&#x90FD;&#x662F;&#x4EE5;CAS&#x5B9E;&#x73B0;&#x7684;&#xFF0C;&#x751A;&#x81F3;ConcurrentHashMap&#x5728;1.8&#x7684;&#x7248;&#x672C;&#x4E2D;&#x4E5F;&#x8C03;&#x6574;&#x4E3A;&#x4E86;CAS+Synchronized&#x3002;&#x53EF;&#x4EE5;&#x8BF4;CAS&#x662F;&#x6574;&#x4E2A;JUC&#x7684;&#x57FA;&#x77F3;&#x3002;</p>
<p><img src="https://gitee.com/zisuu/picture/raw/master/img/20201216081343.png" alt="image-20201216081343080"></p>
<h3 id="cas&#x5206;&#x6790;"><a name="cas&#x5206;&#x6790;" class="anchor-navigation-ex-anchor" href="#cas&#x5206;&#x6790;"><i class="fa fa-link" aria-hidden="true"></i></a><a name="cas&#x5206;&#x6790;" class="plugin-anchor" href="#cas&#x5206;&#x6790;"><i class="fa fa-link" aria-hidden="true"></i></a>CAS&#x5206;&#x6790;</h3>
<p>&#x5728;CAS&#x4E2D;&#x6709;&#x4E09;&#x4E2A;&#x53C2;&#x6570;&#xFF1A;&#x5185;&#x5B58;&#x503C;V&#x3001;&#x65E7;&#x7684;&#x9884;&#x671F;&#x503C;A&#x3001;&#x8981;&#x66F4;&#x65B0;&#x7684;&#x503C;B&#xFF0C;&#x5F53;&#x4E14;&#x4EC5;&#x5F53;&#x5185;&#x5B58;&#x503C;V&#x7684;&#x503C;&#x7B49;&#x4E8E;&#x65E7;&#x7684;&#x9884;&#x671F;&#x503C;A&#x65F6;&#x624D;&#x4F1A;&#x5C06;&#x5185;&#x5B58;&#x503C;V&#x7684;&#x503C;&#x4FEE;&#x6539;&#x4E3A;B&#xFF0C;&#x5426;&#x5219;&#x4EC0;&#x4E48;&#x90FD;&#x4E0D;&#x5E72;&#x3002;&#x5176;&#x4F2A;&#x4EE3;&#x7801;&#x5982;&#x4E0B;&#xFF1A;</p>
<pre><code class="lang-java"><span class="hljs-keyword">if</span>(<span class="hljs-keyword">this</span>.value == A){
    <span class="hljs-keyword">this</span>.value = B
    <span class="hljs-keyword">return</span> <span class="hljs-keyword">true</span>;
}<span class="hljs-keyword">else</span>{
    <span class="hljs-keyword">return</span> <span class="hljs-keyword">false</span>;
}
</code></pre>
<p>JUC&#x4E0B;&#x7684;atomic&#x7C7B;&#x90FD;&#x662F;&#x901A;&#x8FC7;CAS&#x6765;&#x5B9E;&#x73B0;&#x7684;&#xFF0C;&#x4E0B;&#x9762;&#x5C31;&#x4EE5;AtomicInteger&#x4E3A;&#x4F8B;&#x6765;&#x9610;&#x8FF0;CAS&#x7684;&#x5B9E;&#x73B0;&#x3002;&#x5982;&#x4E0B;&#xFF1A;</p>
<pre><code class="lang-java">    <span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">final</span> Unsafe unsafe = Unsafe.getUnsafe();
    <span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-keyword">final</span> <span class="hljs-keyword">long</span> valueOffset;

    <span class="hljs-keyword">static</span> {
        <span class="hljs-keyword">try</span> {
            valueOffset = unsafe.objectFieldOffset
                (AtomicInteger.class.getDeclaredField(<span class="hljs-string">&quot;value&quot;</span>));
        } <span class="hljs-keyword">catch</span> (Exception ex) { <span class="hljs-keyword">throw</span> <span class="hljs-keyword">new</span> Error(ex); }
    }

    <span class="hljs-keyword">private</span> <span class="hljs-keyword">volatile</span> <span class="hljs-keyword">int</span> value;
</code></pre>
<p>Unsafe&#x662F;CAS&#x7684;&#x6838;&#x5FC3;&#x7C7B;&#xFF0C;Java&#x65E0;&#x6CD5;&#x76F4;&#x63A5;&#x8BBF;&#x95EE;&#x5E95;&#x5C42;&#x64CD;&#x4F5C;&#x7CFB;&#x7EDF;&#xFF0C;&#x800C;&#x662F;&#x901A;&#x8FC7;&#x672C;&#x5730;&#xFF08;native&#xFF09;&#x65B9;&#x6CD5;&#x6765;&#x8BBF;&#x95EE;&#x3002;&#x4E0D;&#x8FC7;&#x5C3D;&#x7BA1;&#x5982;&#x6B64;&#xFF0C;JVM&#x8FD8;&#x662F;&#x5F00;&#x4E86;&#x4E00;&#x4E2A;&#x540E;&#x95E8;&#xFF1A;Unsafe&#xFF0C;&#x5B83;&#x63D0;&#x4F9B;&#x4E86;&#x786C;&#x4EF6;&#x7EA7;&#x522B;&#x7684;&#x539F;&#x5B50;&#x64CD;&#x4F5C;&#x3002;</p>
<p>valueOffset&#x4E3A;&#x53D8;&#x91CF;&#x503C;&#x5728;&#x5185;&#x5B58;&#x4E2D;&#x7684;&#x504F;&#x79FB;&#x5730;&#x5740;&#xFF0C;unsafe&#x5C31;&#x662F;&#x901A;&#x8FC7;&#x504F;&#x79FB;&#x5730;&#x5740;&#x6765;&#x5F97;&#x5230;&#x6570;&#x636E;&#x7684;&#x539F;&#x503C;&#x7684;&#x3002;</p>
<p>value&#x5F53;&#x524D;&#x503C;&#xFF0C;&#x4F7F;&#x7528;volatile&#x4FEE;&#x9970;&#xFF0C;&#x4FDD;&#x8BC1;&#x591A;&#x7EBF;&#x7A0B;&#x73AF;&#x5883;&#x4E0B;&#x770B;&#x89C1;&#x7684;&#x662F;&#x540C;&#x4E00;&#x4E2A;&#x3002;</p>
<p>&#x6211;&#x4EEC;&#x5C31;&#x4EE5;AtomicInteger&#x7684;addAndGet()&#x65B9;&#x6CD5;&#x6765;&#x505A;&#x8BF4;&#x660E;&#xFF0C;&#x5148;&#x770B;&#x6E90;&#x4EE3;&#x7801;&#xFF1A;</p>
<pre><code class="lang-java">    <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">final</span> <span class="hljs-keyword">int</span> <span class="hljs-title">addAndGet</span><span class="hljs-params">(<span class="hljs-keyword">int</span> delta)</span> </span>{
        <span class="hljs-keyword">return</span> unsafe.getAndAddInt(<span class="hljs-keyword">this</span>, valueOffset, delta) + delta;
    }

    <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">final</span> <span class="hljs-keyword">int</span> <span class="hljs-title">getAndAddInt</span><span class="hljs-params">(Object var1, <span class="hljs-keyword">long</span> var2, <span class="hljs-keyword">int</span> var4)</span> </span>{
        <span class="hljs-keyword">int</span> var5;
        do {
            var5 = <span class="hljs-keyword">this</span>.getIntVolatile(var1, var2);
        } <span class="hljs-keyword">while</span>(!<span class="hljs-keyword">this</span>.compareAndSwapInt(var1, var2, var5, var5 + var4));

        <span class="hljs-keyword">return</span> var5;
    }
</code></pre>
<p>&#x5185;&#x90E8;&#x8C03;&#x7528;unsafe&#x7684;getAndAddInt&#x65B9;&#x6CD5;&#xFF0C;&#x5728;getAndAddInt&#x65B9;&#x6CD5;&#x4E2D;&#x4E3B;&#x8981;&#x662F;&#x770B;compareAndSwapInt&#x65B9;&#x6CD5;&#xFF1A;</p>
<pre><code class="lang-java">    <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">final</span> <span class="hljs-keyword">native</span> <span class="hljs-keyword">boolean</span> <span class="hljs-title">compareAndSwapInt</span><span class="hljs-params">(Object var1, <span class="hljs-keyword">long</span> var2, <span class="hljs-keyword">int</span> var4, <span class="hljs-keyword">int</span> var5)</span></span>;
</code></pre>
<p>&#x8BE5;&#x65B9;&#x6CD5;&#x4E3A;&#x672C;&#x5730;&#x65B9;&#x6CD5;&#xFF0C;&#x6709;&#x56DB;&#x4E2A;&#x53C2;&#x6570;&#xFF0C;&#x5206;&#x522B;&#x4EE3;&#x8868;&#xFF1A;&#x5BF9;&#x8C61;&#x3001;&#x5BF9;&#x8C61;&#x7684;&#x5730;&#x5740;&#x3001;&#x9884;&#x671F;&#x503C;&#x3001;&#x4FEE;&#x6539;&#x503C;&#x3002;&#x8BE5;&#x65B9;&#x6CD5;&#x7684;&#x5B9E;&#x73B0;&#x8FD9;&#x91CC;&#x5C31;&#x4E0D;&#x505A;&#x8BE6;&#x7EC6;&#x4ECB;&#x7ECD;&#x4E86;&#xFF0C;&#x6709;&#x5174;&#x8DA3;&#x7684;&#x4F19;&#x4F34;&#x53EF;&#x4EE5;&#x770B;&#x770B;openjdk&#x7684;&#x6E90;&#x7801;&#x3002;</p>
<p>CAS&#x53EF;&#x4EE5;&#x4FDD;&#x8BC1;&#x4E00;&#x6B21;&#x7684;&#x8BFB;-&#x6539;-&#x5199;&#x64CD;&#x4F5C;&#x662F;&#x539F;&#x5B50;&#x64CD;&#x4F5C;&#xFF0C;&#x5728;&#x5355;&#x5904;&#x7406;&#x5668;&#x4E0A;&#x8BE5;&#x64CD;&#x4F5C;&#x5BB9;&#x6613;&#x5B9E;&#x73B0;&#xFF0C;&#x4F46;&#x662F;&#x5728;&#x591A;&#x5904;&#x7406;&#x5668;&#x4E0A;&#x5B9E;&#x73B0;&#x5C31;&#x6709;&#x70B9;&#x513F;&#x590D;&#x6742;&#x4E86;&#x3002;</p>
<p>CPU&#x63D0;&#x4F9B;&#x4E86;&#x4E24;&#x79CD;&#x65B9;&#x6CD5;&#x6765;&#x5B9E;&#x73B0;&#x591A;&#x5904;&#x7406;&#x5668;&#x7684;&#x539F;&#x5B50;&#x64CD;&#x4F5C;&#xFF1A;&#x603B;&#x7EBF;&#x52A0;&#x9501;&#x6216;&#x8005;&#x7F13;&#x5B58;&#x52A0;&#x9501;&#x3002;</p>
<ul>
<li><strong>&#x603B;&#x7EBF;&#x52A0;&#x9501;</strong>&#xFF1A;&#x603B;&#x7EBF;&#x52A0;&#x9501;&#x5C31;&#x662F;&#x5C31;&#x662F;&#x4F7F;&#x7528;&#x5904;&#x7406;&#x5668;&#x63D0;&#x4F9B;&#x7684;&#x4E00;&#x4E2A;LOCK#&#x4FE1;&#x53F7;&#xFF0C;&#x5F53;&#x4E00;&#x4E2A;&#x5904;&#x7406;&#x5668;&#x5728;&#x603B;&#x7EBF;&#x4E0A;&#x8F93;&#x51FA;&#x6B64;&#x4FE1;&#x53F7;&#x65F6;&#xFF0C;&#x5176;&#x4ED6;&#x5904;&#x7406;&#x5668;&#x7684;&#x8BF7;&#x6C42;&#x5C06;&#x88AB;&#x963B;&#x585E;&#x4F4F;,&#x90A3;&#x4E48;&#x8BE5;&#x5904;&#x7406;&#x5668;&#x53EF;&#x4EE5;&#x72EC;&#x5360;&#x4F7F;&#x7528;&#x5171;&#x4EAB;&#x5185;&#x5B58;&#x3002;&#x4F46;&#x662F;&#x8FD9;&#x79CD;&#x5904;&#x7406;&#x65B9;&#x5F0F;&#x663E;&#x5F97;&#x6709;&#x70B9;&#x513F;&#x9738;&#x9053;&#xFF0C;&#x4E0D;&#x539A;&#x9053;&#xFF0C;&#x4ED6;&#x628A;CPU&#x548C;&#x5185;&#x5B58;&#x4E4B;&#x95F4;&#x7684;&#x901A;&#x4FE1;&#x9501;&#x4F4F;&#x4E86;&#xFF0C;&#x5728;&#x9501;&#x5B9A;&#x671F;&#x95F4;&#xFF0C;&#x5176;&#x4ED6;&#x5904;&#x7406;&#x5668;&#x90FD;&#x4E0D;&#x80FD;&#x5176;&#x4ED6;&#x5185;&#x5B58;&#x5730;&#x5740;&#x7684;&#x6570;&#x636E;&#xFF0C;&#x5176;&#x5F00;&#x9500;&#x6709;&#x70B9;&#x513F;&#x5927;&#x3002;&#x6240;&#x4EE5;&#x5C31;&#x6709;&#x4E86;&#x7F13;&#x5B58;&#x52A0;&#x9501;&#x3002;</li>
<li><strong>&#x7F13;&#x5B58;&#x52A0;&#x9501;</strong>&#xFF1A;&#x5176;&#x5B9E;&#x9488;&#x5BF9;&#x4E8E;&#x4E0A;&#x9762;&#x90A3;&#x79CD;&#x60C5;&#x51B5;&#x6211;&#x4EEC;&#x53EA;&#x9700;&#x8981;&#x4FDD;&#x8BC1;&#x5728;&#x540C;&#x4E00;&#x65F6;&#x523B;&#x5BF9;&#x67D0;&#x4E2A;&#x5185;&#x5B58;&#x5730;&#x5740;&#x7684;&#x64CD;&#x4F5C;&#x662F;&#x539F;&#x5B50;&#x6027;&#x7684;&#x5373;&#x53EF;&#x3002;&#x7F13;&#x5B58;&#x52A0;&#x9501;&#x5C31;&#x662F;&#x7F13;&#x5B58;&#x5728;&#x5185;&#x5B58;&#x533A;&#x57DF;&#x7684;&#x6570;&#x636E;&#x5982;&#x679C;&#x5728;&#x52A0;&#x9501;&#x671F;&#x95F4;&#xFF0C;&#x5F53;&#x5B83;&#x6267;&#x884C;&#x9501;&#x64CD;&#x4F5C;&#x5199;&#x56DE;&#x5185;&#x5B58;&#x65F6;&#xFF0C;&#x5904;&#x7406;&#x5668;&#x4E0D;&#x5728;&#x8F93;&#x51FA;LOCK#&#x4FE1;&#x53F7;&#xFF0C;&#x800C;&#x662F;&#x4FEE;&#x6539;&#x5185;&#x90E8;&#x7684;&#x5185;&#x5B58;&#x5730;&#x5740;&#xFF0C;&#x5229;&#x7528;&#x7F13;&#x5B58;&#x4E00;&#x81F4;&#x6027;&#x534F;&#x8BAE;&#x6765;&#x4FDD;&#x8BC1;&#x539F;&#x5B50;&#x6027;&#x3002;&#x7F13;&#x5B58;&#x4E00;&#x81F4;&#x6027;&#x673A;&#x5236;&#x53EF;&#x4EE5;&#x4FDD;&#x8BC1;&#x540C;&#x4E00;&#x4E2A;&#x5185;&#x5B58;&#x533A;&#x57DF;&#x7684;&#x6570;&#x636E;&#x4EC5;&#x80FD;&#x88AB;&#x4E00;&#x4E2A;&#x5904;&#x7406;&#x5668;&#x4FEE;&#x6539;&#xFF0C;&#x4E5F;&#x5C31;&#x662F;&#x8BF4;&#x5F53;CPU1&#x4FEE;&#x6539;&#x7F13;&#x5B58;&#x884C;&#x4E2D;&#x7684;i&#x65F6;&#x4F7F;&#x7528;&#x7F13;&#x5B58;&#x9501;&#x5B9A;&#xFF0C;&#x90A3;&#x4E48;CPU2&#x5C31;&#x4E0D;&#x80FD;&#x540C;&#x65F6;&#x7F13;&#x5B58;&#x4E86;i&#x7684;&#x7F13;&#x5B58;&#x884C;&#x3002;</li>
</ul>
<h3 id="cas&#x7F3A;&#x9677;"><a name="cas&#x7F3A;&#x9677;" class="anchor-navigation-ex-anchor" href="#cas&#x7F3A;&#x9677;"><i class="fa fa-link" aria-hidden="true"></i></a><a name="cas&#x7F3A;&#x9677;" class="plugin-anchor" href="#cas&#x7F3A;&#x9677;"><i class="fa fa-link" aria-hidden="true"></i></a>CAS&#x7F3A;&#x9677;</h3>
<p>CAS&#x867D;&#x7136;&#x9AD8;&#x6548;&#x5730;&#x89E3;&#x51B3;&#x4E86;&#x539F;&#x5B50;&#x64CD;&#x4F5C;&#xFF0C;&#x4F46;&#x662F;&#x8FD8;&#x662F;&#x5B58;&#x5728;&#x4E00;&#x4E9B;&#x7F3A;&#x9677;&#x7684;&#xFF0C;&#x4E3B;&#x8981;&#x8868;&#x73B0;&#x5728;&#x4E09;&#x4E2A;&#x65B9;&#x6CD5;&#xFF1A;&#x5FAA;&#x73AF;&#x65F6;&#x95F4;&#x592A;&#x957F;&#x3001;&#x53EA;&#x80FD;&#x4FDD;&#x8BC1;&#x4E00;&#x4E2A;&#x5171;&#x4EAB;&#x53D8;&#x91CF;&#x539F;&#x5B50;&#x64CD;&#x4F5C;&#x3001;ABA&#x95EE;&#x9898;&#x3002;</p>
<p><strong>&#x5FAA;&#x73AF;&#x65F6;&#x95F4;&#x592A;&#x957F;</strong></p>
<p>&#x5982;&#x679C;CAS&#x4E00;&#x76F4;&#x4E0D;&#x6210;&#x529F;&#x5462;&#xFF1F;&#x8FD9;&#x79CD;&#x60C5;&#x51B5;&#x7EDD;&#x5BF9;&#x6709;&#x53EF;&#x80FD;&#x53D1;&#x751F;&#xFF0C;&#x5982;&#x679C;&#x81EA;&#x65CB;CAS&#x957F;&#x65F6;&#x95F4;&#x5730;&#x4E0D;&#x6210;&#x529F;&#xFF0C;&#x5219;&#x4F1A;&#x7ED9;CPU&#x5E26;&#x6765;&#x975E;&#x5E38;&#x5927;&#x7684;&#x5F00;&#x9500;&#x3002;&#x5728;JUC&#x4E2D;&#x6709;&#x4E9B;&#x5730;&#x65B9;&#x5C31;&#x9650;&#x5236;&#x4E86;CAS&#x81EA;&#x65CB;&#x7684;&#x6B21;&#x6570;&#xFF0C;&#x4F8B;&#x5982;BlockingQueue&#x7684;SynchronousQueue&#x3002;</p>
<p><strong>&#x53EA;&#x80FD;&#x4FDD;&#x8BC1;&#x4E00;&#x4E2A;&#x5171;&#x4EAB;&#x53D8;&#x91CF;&#x539F;&#x5B50;&#x64CD;&#x4F5C;</strong></p>
<p>&#x770B;&#x4E86;CAS&#x7684;&#x5B9E;&#x73B0;&#x5C31;&#x77E5;&#x9053;&#x8FD9;&#x53EA;&#x80FD;&#x9488;&#x5BF9;&#x4E00;&#x4E2A;&#x5171;&#x4EAB;&#x53D8;&#x91CF;&#xFF0C;&#x5982;&#x679C;&#x662F;&#x591A;&#x4E2A;&#x5171;&#x4EAB;&#x53D8;&#x91CF;&#x5C31;&#x53EA;&#x80FD;&#x4F7F;&#x7528;&#x9501;&#x4E86;&#xFF0C;&#x5F53;&#x7136;&#x5982;&#x679C;&#x4F60;&#x6709;&#x529E;&#x6CD5;&#x628A;&#x591A;&#x4E2A;&#x53D8;&#x91CF;&#x6574;&#x6210;&#x4E00;&#x4E2A;&#x53D8;&#x91CF;&#xFF0C;&#x5229;&#x7528;CAS&#x4E5F;&#x4E0D;&#x9519;&#x3002;&#x4F8B;&#x5982;&#x8BFB;&#x5199;&#x9501;&#x4E2D;state&#x7684;&#x9AD8;&#x5730;&#x4F4D;</p>
<p><strong>ABA&#x95EE;&#x9898;</strong></p>
<p>CAS&#x9700;&#x8981;&#x68C0;&#x67E5;&#x64CD;&#x4F5C;&#x503C;&#x6709;&#x6CA1;&#x6709;&#x53D1;&#x751F;&#x6539;&#x53D8;&#xFF0C;&#x5982;&#x679C;&#x6CA1;&#x6709;&#x53D1;&#x751F;&#x6539;&#x53D8;&#x5219;&#x66F4;&#x65B0;&#x3002;&#x4F46;&#x662F;&#x5B58;&#x5728;&#x8FD9;&#x6837;&#x4E00;&#x79CD;&#x60C5;&#x51B5;&#xFF1A;&#x5982;&#x679C;&#x4E00;&#x4E2A;&#x503C;&#x539F;&#x6765;&#x662F;A&#xFF0C;&#x53D8;&#x6210;&#x4E86;B&#xFF0C;&#x7136;&#x540E;&#x53C8;&#x53D8;&#x6210;&#x4E86;A&#xFF0C;&#x90A3;&#x4E48;&#x5728;CAS&#x68C0;&#x67E5;&#x7684;&#x65F6;&#x5019;&#x4F1A;&#x53D1;&#x73B0;&#x6CA1;&#x6709;&#x6539;&#x53D8;&#xFF0C;&#x4F46;&#x662F;&#x5B9E;&#x8D28;&#x4E0A;&#x5B83;&#x5DF2;&#x7ECF;&#x53D1;&#x751F;&#x4E86;&#x6539;&#x53D8;&#xFF0C;&#x8FD9;&#x5C31;&#x662F;&#x6240;&#x8C13;&#x7684;ABA&#x95EE;&#x9898;&#x3002;&#x5BF9;&#x4E8E;ABA&#x95EE;&#x9898;&#x5176;&#x89E3;&#x51B3;&#x65B9;&#x6848;&#x662F;&#x52A0;&#x4E0A;&#x7248;&#x672C;&#x53F7;&#xFF0C;&#x5373;&#x5728;&#x6BCF;&#x4E2A;&#x53D8;&#x91CF;&#x90FD;&#x52A0;&#x4E0A;&#x4E00;&#x4E2A;&#x7248;&#x672C;&#x53F7;&#xFF0C;&#x6BCF;&#x6B21;&#x6539;&#x53D8;&#x65F6;&#x52A0;1&#xFF0C;&#x5373;A &#x2014;&gt; B &#x2014;&gt; A&#xFF0C;&#x53D8;&#x6210;1A &#x2014;&gt; 2B &#x2014;&gt; 3A&#x3002;</p>
<p>CAS&#x7684;ABA&#x9690;&#x60A3;&#x95EE;&#x9898;&#xFF0C;&#x89E3;&#x51B3;&#x65B9;&#x6848;&#x5219;&#x662F;&#x7248;&#x672C;&#x53F7;&#xFF0C;Java&#x63D0;&#x4F9B;&#x4E86;AtomicStampedReference&#x6765;&#x89E3;&#x51B3;&#x3002;AtomicStampedReference&#x901A;&#x8FC7;&#x5305;&#x88C5;[E,Integer]&#x7684;&#x5143;&#x7EC4;&#x6765;&#x5BF9;&#x5BF9;&#x8C61;&#x6807;&#x8BB0;&#x7248;&#x672C;&#x6233;stamp&#xFF0C;&#x4ECE;&#x800C;&#x907F;&#x514D;ABA&#x95EE;&#x9898;&#x3002;&#x5BF9;&#x4E8E;&#x4E0A;&#x9762;&#x7684;&#x6848;&#x4F8B;&#x5E94;&#x8BE5;&#x7EBF;&#x7A0B;1&#x4F1A;&#x5931;&#x8D25;&#x3002;</p>
<p>&#x200B;    &#x7684;compareAndSet()&#x65B9;&#x6CD5;&#x5B9A;&#x4E49;&#x5982;&#x4E0B;&#xFF1A;</p>
<pre><code class="lang-java">    <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">boolean</span> <span class="hljs-title">compareAndSet</span><span class="hljs-params">(V   expectedReference,
                                 V   newReference,
                                 <span class="hljs-keyword">int</span> expectedStamp,
                                 <span class="hljs-keyword">int</span> newStamp)</span> </span>{
        Pair&lt;V&gt; current = pair;
        <span class="hljs-keyword">return</span>
            expectedReference == current.reference &amp;&amp;
            expectedStamp == current.stamp &amp;&amp;
            ((newReference == current.reference &amp;&amp;
              newStamp == current.stamp) ||
             casPair(current, Pair.of(newReference, newStamp)));
    }
</code></pre>
<p>compareAndSet&#x6709;&#x56DB;&#x4E2A;&#x53C2;&#x6570;&#xFF0C;&#x5206;&#x522B;&#x8868;&#x793A;&#xFF1A;&#x9884;&#x671F;&#x5F15;&#x7528;&#x3001;&#x66F4;&#x65B0;&#x540E;&#x7684;&#x5F15;&#x7528;&#x3001;&#x9884;&#x671F;&#x6807;&#x5FD7;&#x3001;&#x66F4;&#x65B0;&#x540E;&#x7684;&#x6807;&#x5FD7;&#x3002;&#x6E90;&#x7801;&#x90E8;&#x95E8;&#x5F88;&#x597D;&#x7406;&#x89E3;&#x9884;&#x671F;&#x7684;&#x5F15;&#x7528; == &#x5F53;&#x524D;&#x5F15;&#x7528;&#xFF0C;&#x9884;&#x671F;&#x7684;&#x6807;&#x8BC6; == &#x5F53;&#x524D;&#x6807;&#x8BC6;&#xFF0C;&#x5982;&#x679C;&#x66F4;&#x65B0;&#x540E;&#x7684;&#x5F15;&#x7528;&#x548C;&#x6807;&#x5FD7;&#x548C;&#x5F53;&#x524D;&#x7684;&#x5F15;&#x7528;&#x548C;&#x6807;&#x5FD7;&#x76F8;&#x7B49;&#x5219;&#x76F4;&#x63A5;&#x8FD4;&#x56DE;true&#xFF0C;&#x5426;&#x5219;&#x901A;&#x8FC7;Pair&#x751F;&#x6210;&#x4E00;&#x4E2A;&#x65B0;&#x7684;pair&#x5BF9;&#x8C61;&#x4E0E;&#x5F53;&#x524D;pair CAS&#x66FF;&#x6362;&#x3002;Pair&#x4E3A;AtomicStampedReference&#x7684;&#x5185;&#x90E8;&#x7C7B;&#xFF0C;&#x4E3B;&#x8981;&#x7528;&#x4E8E;&#x8BB0;&#x5F55;&#x5F15;&#x7528;&#x548C;&#x7248;&#x672C;&#x6233;&#x4FE1;&#x606F;&#xFF08;&#x6807;&#x8BC6;&#xFF09;&#xFF0C;&#x5B9A;&#x4E49;&#x5982;&#x4E0B;&#xFF1A;</p>
<pre><code class="lang-java">    <span class="hljs-keyword">private</span> <span class="hljs-keyword">static</span> <span class="hljs-class"><span class="hljs-keyword">class</span> <span class="hljs-title">Pair</span>&lt;<span class="hljs-title">T</span>&gt; </span>{
        <span class="hljs-keyword">final</span> T reference;
        <span class="hljs-keyword">final</span> <span class="hljs-keyword">int</span> stamp;
        <span class="hljs-function"><span class="hljs-keyword">private</span> <span class="hljs-title">Pair</span><span class="hljs-params">(T reference, <span class="hljs-keyword">int</span> stamp)</span> </span>{
            <span class="hljs-keyword">this</span>.reference = reference;
            <span class="hljs-keyword">this</span>.stamp = stamp;
        }
        <span class="hljs-keyword">static</span> &lt;T&gt; <span class="hljs-function">Pair&lt;T&gt; <span class="hljs-title">of</span><span class="hljs-params">(T reference, <span class="hljs-keyword">int</span> stamp)</span> </span>{
            <span class="hljs-keyword">return</span> <span class="hljs-keyword">new</span> Pair&lt;T&gt;(reference, stamp);
        }
    }

    <span class="hljs-keyword">private</span> <span class="hljs-keyword">volatile</span> Pair&lt;V&gt; pair;
</code></pre>
<p>Pair&#x8BB0;&#x5F55;&#x7740;&#x5BF9;&#x8C61;&#x7684;&#x5F15;&#x7528;&#x548C;&#x7248;&#x672C;&#x6233;&#xFF0C;&#x7248;&#x672C;&#x6233;&#x4E3A;int&#x578B;&#xFF0C;&#x4FDD;&#x6301;&#x81EA;&#x589E;&#x3002;&#x540C;&#x65F6;Pair&#x662F;&#x4E00;&#x4E2A;&#x4E0D;&#x53EF;&#x53D8;&#x5BF9;&#x8C61;&#xFF0C;&#x5176;&#x6240;&#x6709;&#x5C5E;&#x6027;&#x5168;&#x90E8;&#x5B9A;&#x4E49;&#x4E3A;final&#xFF0C;&#x5BF9;&#x5916;&#x63D0;&#x4F9B;&#x4E00;&#x4E2A;of&#x65B9;&#x6CD5;&#xFF0C;&#x8BE5;&#x65B9;&#x6CD5;&#x8FD4;&#x56DE;&#x4E00;&#x4E2A;&#x65B0;&#x5EFA;&#x7684;Pari&#x5BF9;&#x8C61;&#x3002;pair&#x5BF9;&#x8C61;&#x5B9A;&#x4E49;&#x4E3A;volatile&#xFF0C;&#x4FDD;&#x8BC1;&#x591A;&#x7EBF;&#x7A0B;&#x73AF;&#x5883;&#x4E0B;&#x7684;&#x53EF;&#x89C1;&#x6027;&#x3002;&#x5728;AtomicStampedReference&#x4E2D;&#xFF0C;&#x5927;&#x591A;&#x65B9;&#x6CD5;&#x90FD;&#x662F;&#x901A;&#x8FC7;&#x8C03;&#x7528;Pair&#x7684;of&#x65B9;&#x6CD5;&#x6765;&#x4EA7;&#x751F;&#x4E00;&#x4E2A;&#x65B0;&#x7684;Pair&#x5BF9;&#x8C61;&#xFF0C;&#x7136;&#x540E;&#x8D4B;&#x503C;&#x7ED9;&#x53D8;&#x91CF;pair&#x3002;&#x5982;set&#x65B9;&#x6CD5;&#xFF1A;</p>
<pre><code class="lang-java">    <span class="hljs-function"><span class="hljs-keyword">public</span> <span class="hljs-keyword">void</span> <span class="hljs-title">set</span><span class="hljs-params">(V newReference, <span class="hljs-keyword">int</span> newStamp)</span> </span>{
        Pair&lt;V&gt; current = pair;
        <span class="hljs-keyword">if</span> (newReference != current.reference || newStamp != current.stamp)
            <span class="hljs-keyword">this</span>.pair = Pair.of(newReference, newStamp);
    }
</code></pre>
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